Technical Abstract:
Biosolids have been applied to agricultural land for many years as a source of plant nutrients. There is concern, however, that long-term use of biosolids could increase soil phosphorus to levels, which threaten surface water due to P runoff, leaching or erosion. The objectives of this study were to 1) determine the solubility of P in long-term biosolids amended and control soils and 2) estimate P availability for wheat growth. Wheat was grown in 15x15 cm pots with three soils from Maryland, Minnesota, and Illinois that were amended with biosolids from different sources and methods of treatment. Nitrogen, Mg and K fertilizers were applied two weeks after planting. Phosphorus concentrations in the soil increased with biosolids application; for example, water extractable P ranged from 3.6-6.3, 1.4-6.7 and 1.4-4.0 mg kg-1 and Mehlich-3 extractable P ranged from 164-568, 61- 228 and 74-623 mg kg-1 for the Maryland, Minnesota and Illinois soil respectively. Yield also increased with biosolid application compared to the control soil with the exception of the Illinois soil and the limed composted biosolid on the Maryland soil in which the yields did not change or significantly lower than the control. For example the yield for the control Maryland soil was 9.5 g/pot compared to 2.0 g/pot for the limed composted biosolids. This yield reduction is attributed to manganese deficiency, because foliar Mn was 2.7 mg kg-1 compared to 14.8 mg kg-1 for the control Maryland soil. Phosphorus concentrations in the tissue were at sufficient levels for wheat tissue even though P fertilizers had not been applied for many years. Land application of biosolids may increase the potential for eutrophication of surface water. However, we believe that assessment of P risk using water extractable P should be used rather than soil test methods which greatly over-estimate potential P runoff.